Papers by Josefine Axelsson
Authorea (Authorea), Feb 1, 2023
• Direct measurements of event-based δ 18 O and d-excess in precipitation in the central Himalaya... more • Direct measurements of event-based δ 18 O and d-excess in precipitation in the central Himalayas in the 2015 monsoon season compared to 2014. • Combination of in-situ isotopic measurements with simulations of evaporation minus precipitation (E-P) using FLEXPART. • Isotopic variations in precipitation are associated with changes in moisture supplies along the transport path.
<p>Due to age uncertainties and poor resolution in speleothems, age-depth modelling techniq... more <p>Due to age uncertainties and poor resolution in speleothems, age-depth modelling techniques are often implemented for cross-examinations. In this study, we use a variation of the analogue method to perform a pseudo-proxy reconstruction of the large-scale variability in Indian and East Asian monsoon precipitation using synthetic oxygen isotope records from speleothem sites and an isotope-enabled climate model.</p><p>We present a probabilistic approach to synchronize speleothems through oxygen isotope data and individual independent age constraints, achieved by co-estimating the regional &#948;18O variations through time. The &#948;18O variability is modelled using Gaussian processes, and an adaptation of BACON age-depth model is further used for the individual speleothem chronologies.</p><p>The method is tested using synthetic speleothem data generated from the ECHAM/MPI-OM climate model and corrupted through realistic noise from speleothems from the SISAL database.</p><p>By incorporating accurate and realistic depth-dependent age-uncertainties rather than shifting, stretching or compressing the time-series of oxygen isotope data, this modelling approach may lead to advancements of handling speleothem data for regional to global evaluations on variability between speleothems and timescales.</p>
Observational data from the past century show a weakening trend in summer monsoon over the Indian... more Observational data from the past century show a weakening trend in summer monsoon over the Indian subcontinent. This is possibly attributed to the reduced land–sea contrast resulting from the India...
Geophysical Research Letters, Mar 14, 2022
Paleoclimate proxy data indicate a stronger Indian summer monsoon (ISM) during the Last Interglac... more Paleoclimate proxy data indicate a stronger Indian summer monsoon (ISM) during the Last Interglacial (LIG) than in the present day. This is largely attributed to orbital forcing induced high seasonal and latitudinal insolation anomalies in the Northern Hemisphere during LIG. According to the general circulation model EC‐Earth3, the simulated ISM rainfall is increased by approximately 28% during the LIG compared to the pre‐industrial period as a result of the orbital forcing and the amplified land‐sea contrast due to both local and remote ocean feedbacks. Although the LIG is often portrayed as a potential analogue of future warmer climates, our study suggests that the enhanced inter‐hemispheric thermal gradient during the LIG strengthened the ISM, in opposition to the observed weakening of ISM under present‐day warming.
Climate of The Past, Jul 13, 2022
The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) ... more The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modeled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modeled water isotopologues, as well as the diversity of their representation in different models, are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable terrestrial paleoclimate archives and provide wellpreserved (semi-)continuous multivariate isotope time series in the lower latitudes and mid-latitudes and are therefore well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationships of speleothem oxygen and carbon isotopes to climate variables are influenced by site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and Analysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850-1850 CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of Published by Copernicus Publications on behalf of the European Geosciences Union. 1626 J. C. Bühler et al.: SISALv2 last millennium multi-model data comparison variability for modeled isotopes and compare them to those of measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modeled surface temperature. At low latitudes, precipitation amount is the dominant driver for stable water isotope variability; however, at cave locations the agreement between modeled temperature variability is higher than for precipitation variability. While modeled isotopic signatures at cave locations exhibited extreme events coinciding with changes in volcanic and solar forcing, such fingerprints are not apparent in the speleothem isotopes. This may be attributed to the lower temporal resolution of speleothem records compared to the events that are to be detected. Using spectral analysis, we can show that all models underestimate decadal and longer variability compared to speleothems (albeit to varying extents). We found that no model excels in all analyzed comparisons, although some perform better than the others in either mean or variability. Therefore, we advise a multimodel approach whenever comparing proxy data to modeled data. Considering karst and cave internal processes, e.g., through isotope-enabled karst models, may alter the variability in speleothem isotopes and play an important role in determining the most appropriate model. By exploring new ways of analyzing the relationship between the oxygen and carbon isotopes, their variability, and co-variability across timescales, we provide methods that may serve as a baseline for future studies with different models using, e.g., different isotopes, different climate archives, or different time periods.
List of Tables ST1 Linear regression between isotopes, simulated climate variables and geographic... more List of Tables ST1 Linear regression between isotopes, simulated climate variables and geographical information with 90%
The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) ... more The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modelled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modelled water isotopologues, and indeed the diversity of their representation in different models are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable paleoclimate archive and provide well preserved (semi-)continuous multivariate isotope time series in the lower and mid-latitudes, and are, therefore, well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationship between speleothem oxygen and carbon isotopes to climate variables also depends on site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and AnaLysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850-1850 common era, CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of variability for both modelled and measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modelled temperatures. At low latitudes, precipitation amount is the dominant driver for water isotope variability, however, at cave locations the agreement between modelled temperature variability is higher than for precipitation variability. While modelled isotopic signatures at cave locations exhibited extreme events coinciding with changes in volcanic and solar forcing, such fingerprints are not apparent in the speleothem isotopes, and may be attributed to the lower temporal resolution 1
Quaternary, Jun 26, 2020
Irregular climate events frequently occur in Southeast Asia due to the numerous climate patterns ... more Irregular climate events frequently occur in Southeast Asia due to the numerous climate patterns combining. Thailand sits at the confluence of these interactions, and consequently experiences major hydrological events, such as droughts. Proxy data, speleothem records, lake sediment sequences and tree ring chronologies were used to reconstruct paleo drought conditions. These trends were compared with modelled and historic El Niño Southern Oscillation (ENSO) data to assess if the ENSO climate phenomena is causing droughts in Thailand. Drought periods were found to occur both during El Niño events and ENSO neutral conditions. This indicates droughts are not a product of one climate pattern, but likely the result of numerous patterns interacting. There is uncertainty regarding how climate patterns will evolve under climate change, but changes in amplitude and variability could potentially lead to more frequent and wider reaching hydrological disasters. It is vital that policies are implemented to cope with the resulting social and economic repercussions, including diversification of crops and reorganisation of water consumption behaviour in Thailand.
Nature Communications
Qunf Cave oxygen isotope (δ18Oc) record from southern Oman is one of the most significant of few ... more Qunf Cave oxygen isotope (δ18Oc) record from southern Oman is one of the most significant of few Holocene Indian summer monsoon cave records. However, the interpretation of the Qunf δ18Oc remains in dispute. Here we provide a multi-proxy record from Qunf Cave and climate model simulations to reconstruct the Holocene local and regional hydroclimate changes. The results indicate that besides the Indian summer monsoon, the North African summer monsoon also contributes water vapor to southern Oman during the early to middle Holocene. In principle, Qunf δ18Oc values reflect integrated oxygen-isotope fractionations over a broad moisture transport swath from moisture sources to the cave site, rather than local precipitation amount alone, and thus the Qunf δ18Oc record characterizes primary changes in the Afro-Asian monsoon regime across the Holocene. In contrast, local climate proxies appear to suggest an overall slightly increased or unchanged wetness over the Holocene at the cave site.
Journal Of Geophysical Research: Atmospheres, Jul 6, 2023
The effect of moisture transport on precipitation stable isotopes (δO and d-excess) in the centra... more The effect of moisture transport on precipitation stable isotopes (δO and d-excess) in the central Himalayas is still unclear, although crucial to understand the climatic archives recorded in, e.g., ice cores. Here we present measurements of stable isotopes in precipitation at two stations (Yadong and Pali) in the central Himalayas during 2014-2015. Combined with simulations from the dispersion model FLEXPART, we investigate possible effects on precipitation stable isotopes related to changes in moisture sources and convections in the region. Here we show that precipitation stable isotopes and convective activities are different between 2014 and the El Niño year 2015 in Yadong Valley. Our results show that enriched O and high d-excess in precipitation during the 2015 monsoon season compared to 2014 is accompanied by a change in δO lapse rate as an outcome of changes in upstream convection which alters δO through kinetic fractionation. During 2015, isotopic variations are linked to larger contributions of moisture from the Arabian Sea and the Indian continent, as well as lesser from the Bay of Bengal (BoB). Outgoing longwave radiation and moisture flux divergence analysis further confirms that contribution from continental evaporation dominates the moisture supply in the central Himalayas with a lesser contribution from convection over the BoB during the 2015 monsoon season, compared with 2014. These findings provide insights into climatic interpretations of paleo-isotopic archives regarding responses to changes in moisture transport to the central Himalayas.
The effect of moisture transport on precipitation stable isotopes (δO and d-excess) in the centra... more The effect of moisture transport on precipitation stable isotopes (δO and d-excess) in the central Himalayas is still unclear, although crucial to understand the climatic archives recorded in, e.g., ice cores. Here we present measurements of stable isotopes in precipitation at two stations (Yadong and Pali) in the central Himalayas during 2014-2015. Combined with simulations from the dispersion model FLEXPART, we investigate possible effects on precipitation stable isotopes related to changes in moisture sources and convections in the region. Here we show that precipitation stable isotopes and convective activities are different between 2014 and the El Niño year 2015 in Yadong Valley. Our results show that enriched O and high d-excess in precipitation during the 2015 monsoon season compared to 2014 is accompanied by a change in δO lapse rate as an outcome of changes in upstream convection which alters δO through kinetic fractionation. During 2015, isotopic variations are linked to l...
Geophysical Research Letters, 2022
Paleoclimate proxy data indicate a stronger Indian summer monsoon (ISM) during the Last Interglac... more Paleoclimate proxy data indicate a stronger Indian summer monsoon (ISM) during the Last Interglacial (LIG) than in the present day. This is largely attributed to orbital forcing induced high seasonal and latitudinal insolation anomalies in the Northern Hemisphere during LIG. According to the general circulation model EC‐Earth3, the simulated ISM rainfall is increased by approximately 28% during the LIG compared to the pre‐industrial period as a result of the orbital forcing and the amplified land‐sea contrast due to both local and remote ocean feedbacks. Although the LIG is often portrayed as a potential analogue of future warmer climates, our study suggests that the enhanced inter‐hemispheric thermal gradient during the LIG strengthened the ISM, in opposition to the observed weakening of ISM under present‐day warming.
Climate of the Past
The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) ... more The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modeled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modeled water isotopologues, as well as the diversity of their representation in different models, are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable terrestrial paleoclimate archives and provide wellpreserved (semi-)continuous multivariate isotope time series in the lower latitudes and mid-latitudes and are therefore well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationships of speleothem oxygen and carbon isotopes to climate variables are influenced by site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and Analysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850-1850 CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of Published by Copernicus Publications on behalf of the European Geosciences Union. 1626 J. C. Bühler et al.: SISALv2 last millennium multi-model data comparison variability for modeled isotopes and compare them to those of measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modeled surface temperature. At low latitudes, precipitation amount is the dominant driver for stable water isotope variability; however, at cave locations the agreement between modeled temperature variability is higher than for precipitation variability. While modeled isotopic signatures at cave locations exhibited extreme events coinciding with changes in volcanic and solar forcing, such fingerprints are not apparent in the speleothem isotopes. This may be attributed to the lower temporal resolution of speleothem records compared to the events that are to be detected. Using spectral analysis, we can show that all models underestimate decadal and longer variability compared to speleothems (albeit to varying extents). We found that no model excels in all analyzed comparisons, although some perform better than the others in either mean or variability. Therefore, we advise a multimodel approach whenever comparing proxy data to modeled data. Considering karst and cave internal processes, e.g., through isotope-enabled karst models, may alter the variability in speleothem isotopes and play an important role in determining the most appropriate model. By exploring new ways of analyzing the relationship between the oxygen and carbon isotopes, their variability, and co-variability across timescales, we provide methods that may serve as a baseline for future studies with different models using, e.g., different isotopes, different climate archives, or different time periods.
. The incorporation of water isotopologues into the hydrology of general circulation models (GCMs... more . The incorporation of water isotopologues into the hydrology of general circulation models (GCMs) facilitates the comparison between modelled and measured proxy data in paleoclimate archives. However, the variability and drivers of measured and modelled water isotopologues, and indeed the diversity of their representation in different models are not well constrained. Improving our understanding of this variability in past and present climates will help to better constrain future climate change projections and decrease their range of uncertainty. Speleothems are a precisely datable paleoclimate archive and provide well preserved (semi-)continuous multivariate isotope time series in the lower and mid-latitudes, and are, therefore, well suited to assess climate and isotope variability on decadal and longer timescales. However, the relationship between speleothem oxygen and carbon isotopes to climate variables also depends on site-specific parameters, and their comparison to GCMs is not always straightforward. Here we compare speleothem oxygen and carbon isotopic signatures from the Speleothem Isotopes Synthesis and AnaLysis database version 2 (SISALv2) to the output of five different water-isotope-enabled GCMs (ECHAM5-wiso, GISS-E2-R, iCESM, iHadCM3, and isoGSM) over the last millennium (850–1850 common era, CE). We systematically evaluate differences and commonalities between the standardized model simulation outputs. The goal is to distinguish climatic drivers of variability for both modelled and measured isotopes. We find strong regional differences in the oxygen isotope signatures between models that can partly be attributed to differences in modelled temperatures. At low latitudes, precipitation amount is the dominant driver for water isotope variability, however, at cave locations the agreement between modelled temperature variability is higher than for precipitation variability. While modelled isotopic signatures at cave locations exhibited extreme events coinciding with changes in volcanic and solar forcing, such fingerprints are not apparent in the speleothem isotopes, and may be attributed to the lower temporal resolution of speleothem records compared to the events that are to be detected. Using spectral analysis, we can show that all models underestimate decadal and longer variability compared to speleothems, although to varying extent. We found that no model excels in all analyzed comparisons, although some perform better than the others in either mean or variability. Therefore, we advise a multi-model approach, whenever comparing proxy data to modelled data. Considering karst and cave internal processes through e.g. isotope-enabled karst models may alter the variability in speleothem isotopes and play an important role in determining the most appropriate model. By exploring new ways of analyzing the relationship between the oxygen and carbon isotopes, their variability, and co-variability across timescales, we provide methods that may serve as a baseline for future studies with different models using e.g. different isotopes, different climate archives, or time periods.
Observational data from the past century show a weakening trend in summer monsoon over the Indian... more Observational data from the past century show a weakening trend in summer monsoon over the Indian subcontinent. This is possibly attributed to the reduced land–sea contrast resulting from the India...
Paleoclimate modelling has long been regarded as a strong out-of-sample test-bed of the climate m... more Paleoclimate modelling has long been regarded as a strong out-of-sample test-bed of the climate models that are used for the projection of future climate changes. For the first time, the EC-Earth model contributes to the Paleoclimate Model Intercomparison Project (PMIP) phase 4, which is part of the current sixth phase of the Coupled Model Intercomparison Project (CMIP6). Here, we document the model setup for PMIP4 experiments with EC-Earth3-LR and present the results on the large-scale features from the completed production simulations 15 for the three past warm periods (mid-Holocene, Last Interglacial, and mid-Pliocene). Using the pre-industrial climate as a reference state, we show the changes in global temperature, large scale Hadley circulation and Walker circulation, polar warming and global monsoons, as well as the climate variability modes (ENSO, PDO, AMO). The EC-Earth3-LR simulates reasonable climate responses during past warm periods as shown in the other PMIP4-CMIP6 mode...
Geoscientific Model Development, 2021
Abstract. As global warming is proceeding due to rising greenhouse gas concentrations, the Earth ... more Abstract. As global warming is proceeding due to rising greenhouse gas concentrations, the Earth system moves towards climate states that challenge adaptation. Past Earth system states are offering possible modelling systems for the global warming of the coming decades. These include the climate of the mid-Pliocene ( ∼ 3 Ma), the last interglacial ( ∼ 129–116 ka) and the mid-Holocene ( ∼ 6 ka). The simulations for these past warm periods are the key experiments in the Paleoclimate Model Intercomparison Project (PMIP) phase 4, contributing to phase 6 of the Coupled Model Intercomparison Project (CMIP6). Paleoclimate modelling has long been regarded as a robust out-of-sample test bed of the climate models used to project future climate changes. Here, we document the model setup for PMIP4 experiments with EC-Earth3-LR and present the large-scale features from the simulations for the mid-Holocene, the last interglacial and the mid-Pliocene. Using the pre-industrial climate as a refer...
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Papers by Josefine Axelsson